Solder Wick: Design Rules and Process Limits
Solder wick is a braided copper strip that is heated on a joint and draws the molten alloy into itself by capillary action. It is the standard way to remove solder from a joint, and the way it is used decides whether the pad survives.
How the Wick Works
The braid has a large surface area and a fine capillary path, so molten alloy travels into it as soon as it wets. The wick is heated from above and the heat passes through it to the joint underneath.
The alloy therefore has to be molten before the wick can take it, which means the wick competes with the joint for the heat that the iron supplies. Our joint criteria notes define the joint that follows the rework.
Points to Confirm at First Article
The acceptance criteria should be written before the work starts, so that the decision is made by the specification rather than by the person inspecting. The environment around the process, including temperature, humidity and cleanliness, sets limits on what the process can hold.
A result that cannot be reproduced is not a result, and reproducibility should be demonstrated rather than assumed. The tooling, the material and the profile form one system, and a change to any of them should be assessed against the other two before it is released.
Handling between operations is part of the process, and the damage it causes is often attributed to the operation that preceded it. A change that is not recorded is a change that cannot be explained when the result moves, which is why the record is part of the process.
The checks that matter are the ones performed on the product rather than on a sample kept for the purpose, because a coupon that travels with the panel is the only evidence about that panel. Where an operation cannot be verified afterwards, it has to be controlled during the operation, and that control has to be visible in the record.
Consumables have a life measured in cycles, and the replacement point should come from the measurement rather than from a failure.
Documented Process Control
The narrowest feature on the board usually sets the process window for the whole product, so it deserves the closest attention at review. A record that identifies the operator, the date and the settings is worth more than a record that identifies only the result.
Where the supplier and the user both measure the same property, they should agree on the method before the first delivery. Sampling is a compromise between cost and confidence, and the sample size should follow from the failure rate that has to be detected.
Flux and Its Role in the Wick
The wick has to wet before the joint does, and the flux is what makes that happen. A wick with an active flux draws alloy readily and a dry wick sits on top of a molten joint without taking anything.
The flux residue left behind is the second consideration, because it has to be compatible with the assembly. A wick whose flux leaves a residue that cannot be cleaned is a problem on a no-clean product. Our first pass yield notes describe how that appears in the data.
The iron adds heat to the wick and the wick takes heat away as alloy enters it. That balance sets the dwell, and a dwell that is too long damages the pad and the laminate without removing more alloy.
The practical approach is a hot iron, a short dwell and a fresh piece of wick for each joint. A wick that is already full removes almost nothing and continues to draw heat. Our profile notes describe the same thermal reasoning in a different process.
<img src="https://www.gopcba.com/wp-content/uploads/2026/08/low-volume-pcb-aoi-xray-testing-early-defect-detection.jpg.webp" alt="Desoldering nozzle used instead of braid” />
A pad can take a limited number of wicking operations before the adhesion fails or the copper thins. The limit is not published and it is experienced, which is why the operation is recorded.
The damage appears as a lifted pad or as a pad that has lost a visible amount of copper. Both are visible after the operation and neither is visible during it.
A desoldering tool with a vacuum nozzle removes alloy without a braid, and it leaves less residue and less thermal damage. It is less effective on a joint that is hard to reach and it needs its own tip for each joint type.
Hot air with a vacuum is used on a through hole part and on an array. The choice follows the joint rather than the bench. Our board quality notes describe how the reworked board is judged.
The rules that preserve the board are a fresh piece of wick per joint, a defined iron temperature, a short dwell, a preheat where the joint has a thermal mass, and a record of the number of operations on a site.
The preheat is the one that is most often omitted, and it is the one that most reduces the dwell. A joint that has been preheated needs less time under the iron for the same result.
Can the same wick be reused? It can be cut and reused, and a full section removes nothing, so a fresh piece per joint is the practical rule.
Does the wick remove all the solder? It removes what is molten and the joint is left tinned rather than bare, which is what the following operation expects.
What does gopcb provide for desoldering? We provide wick and flux selected for the assembly and its cleaning requirement, iron temperature and dwell defined at the station, preheat applied to joints with thermal mass, the number of operations recorded per site, and the reworked joint inspected to the original criteria.
Checks Before Release
Where a requirement can be measured, it should be measured at the point of manufacture and recorded against the board or the lot it applies to. A parameter that is set once and never re verified drifts, and the drift is usually discovered by a defect rather than by the record.
Where the process window is narrow, the measurement resolution has to be better than the window, or the data cannot distinguish a good part from a marginal one.
